Certain actuators use a wave gear device as a reducer for reducing and outputting the rotation of a motor. A known example of a controller for controlling the positioning of an actuator of this configuration is a semi-closed loop control system in which the rotational position and rotational speed of a motor shall are detected by an encoder attached to the motor shall, and are used as a basis for controlling the rotation of a load shaft, which is the output shall of the reducer. In a semi-closed loop control system, the characteristics of the wave gear device have a great effect on the positioning control characteristics of the load shaft because the driving of the motor is not controlled by directly detecting the rotational information of the load shaft.
The wave gear device has nonlinear spring characteristics and nonlinear friction that come with hysteresis due to a unique structure that uses the elastic deformation of the gear thereof. The vibration or angular transmission error (relative rotation-synchronous component) that occurs synchronously with rotation due to gear machining errors or assembly errors causes steady state deviation or vibration, particularly in the load position of the semi-closed loop control system. Therefore, a control system that can uniformly compensate such nonlinear characteristics is needed in order to achieve high precision control of the load shaft.
Exact linearization methods for input/output relationships are known as examples of methods for controlling objects to be controlled including nonlinear elements. FIG. 6 shows a block line diagram of exact linearization. Exact linearization is a method in which a nonlinear plant model having a nonlinear relationship within a state equation is constructed for an object to be controlled including nonlinear elements, linearization feedback α(x) and input conversion β(x) are applied, and the object to be controlled is linearized using no approximation by establishing, from the input v of an expanded system including α(x) and β(x), the values of α(x), β(x) at which the characteristics of the output y will be dny/dtn=v (Non-patent Document 1).